Induction-motor.



B. McCOLLUM.

INDUCTION MOTOR.

APPLICATION FILED FEB. 25. 1915.

1,156,364. Patented Oct. 12, 1915.

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UNITED STATES PATENT GFFICE.

BURTON MQCOLLUM, OF \VASHINGTON, DISTRICT OF COLUMBIA.

INDUCTION-MOTOR.

Application fi1ed February 25, 1915.

To all whom it may concern:

Be it known that I, BURTON MoCoLLUM, a citizen of the United States, and a resident of Washington, in the District of Columbia, have invented a new and useful Improvement in Induction-Motors, of which the following is a specification.

My invention has for its object the production of a rotor of the squirrel cage type which will possess all of the mechanical simplicity and ruggedness and low first cost characteristic of the usual type of squirrel cage rotor, and which will at the same time possess the inherent property of having a high resistance during the starting period but a relatively low resistance under normal running conditions. It is well known that such a property would enable the motor to give a high starting torque and low starting current combined with high efficiency and small speed regulation under normal load conditions, something which cannot be accomplished with the usual type of squirrel cage rotor.

My invention is a modification of my previous inventions described in U. S. Letters Patents Nos. 1,088,77 5, dated September 17, 1912, 1,044,217, dated November 12, 1912, 1,049,506, dated January 7, 1913, and 1,082,603, dated December 30, 1913. My invention makes use of the same principle as described in the above mentioned patents and involves a particular embodiment of those principles with the view of simplifying and cheapening the construction, and producing a stronger and more rugged mechanical structure.

My invention is described in detail below, reference being made to the accompanying drawings.

Of the drawings: Figure 1 shows in detail a construction embodying one practical form of my invention. Fig. 2 is a view of the resistor element only, showing certaindetails. Fig. 3 is a slightly modified form of the resistor element shown in Fig. 2. Fi l is a sectional view of a slightly modified form of my invention.

Referring to Fig. 1, 1 is the usual laminated core mounted on the shaft 2 and carrying the conductor bars 3 of the squirrel cage. A low resistance short circuiting ring is here shown made of two parts 4 and 5, between which is placed the disk 6, a portion of which forms a resistor 6 of high temperature coeflicient of resistance, inter- Specification of Letters Patent.

Patented Oct. 12, 1915.

Serial No. 10,607.

posed between, and mechanically and electrically connected to, both the bars 3 and the low resistance rings 4: and 5. he rings 1 and 5 and the disk 6 are preferably fastened together into a single piece by soldering, b 'azing or welding, or by any other means insuring a permanent mechanical and electrical union. Mounted on the outer surface 01 the rings 4: and 5 respectively, are the rings 7 and S, which may press close against the disk 6 but should not make a good electrical connection therewith. Both the rings 7 and 8 are cut away on the side adjoining the disk 6 as shown at 9. Both the disk 6 and the ring 7 are mechanically connected to the bars 3 by riveting as here shown, or by any other suitable means, and the disk 6 is further connected to the bars 3 in a manner to insure a permanent electrical connection as above stated. as by soldering, brazing or welding. It is desirable to compel most of the current from the bars 8 to go through the portion 6 of the disk 6 to the low resistance rings 4 and 5, and hence it is important that the construction be such that the rings 7 and 8 will not exert any detrimental shunting action on the resister element 6. Such shunting action can be substantially prevented by" making the rings 7 and 8 of a metal having a very high resistivity, such for example, as any of the well known high resistance alloys, and by further producing on all adjoining surfaces a high resistance layer as by tarnishing the surfaces before putting them together, or

by applying a layer of insulating material.

equivalent to a solid metal ring, but the tarnished surfaces of contact combined with the high resistivity of the rings 7 and 8 afford such a high resistance that there is no material shunting of the current away from the resistor element 6. This resistor is made of a material having a high positive temperature coefiicient .of resistance, and

preferably characterized by an abrupt rise of resistance at a critical value of current, and should be so proportioned that the normal full load. currents and usual overload currents are below the critical value of current, while the relatively high starting cur rents are above this critical value. The resistor 6 will then have a relatively low resistance under all normal load conditions, and a relatively high resistance at low speeds and at starting, thus giving a high starting torque to the motor, and at the same time permitting high efficiency and small speed regulation. The ring 7 is here shown fastened to the bars 3 by riveting, accomplished by extending the reduced ends of the bars 3 through perforations in the ring 7 and upsetting the ends of the bars as shown at .12. Screws or any other suitable means may however be used if desired. In Fig. 1 there is shown a ring fastened to the ring a by screws 11, and overlapping the inner edge of the ring 7, thereby tend-- ing to hold it in place relative to the ring 1, but if the ring 7 is shrunk on hot as above described, the ring 10 will not be necessary.

Fig. 2 shows some details of construction of the resistor 6. In this figure, there is shown an outer portion 6, a central portion 6', and an inner portion 6". The outer and inner portions 6 and 6 are preferably copper plated, since both of these portions are to be electrically connected to other parts. The central portion 6-constitutes the resister proper, and this should not be copper plated, but may, if desired, be coated with a material which resists oxidation at high temperatures, as explained later. The outer portion of the disk has perforations 13, through which project the reduced ends of the bars of the squirrel cage.

Fig. 3 shows a modified form of the resistor element in which radial slots 14 are provided in the portion 6 so as to permit thermal expansion in a tangential direction without warping of the disk such as would otherwise occur if a thin disk were used.

Fig. at shows a slightly modified form of the structure shown in Fig. 1. Here there is interposed between the ring 7 and the portion 4 of the low resistance short circuiting ring, the additional rings 15. There may be any number of these rings desired, and they may be shrunk on hot as previously described. Similarly, the rings 16 are interposed between the ring 8 and the ring 5. The object of these additional rings is to introduce additional contact resistances in the paths shunting the resistor element 6, and by this means, the shunting effect can be practically eliminated. The rings 15 and 16 may be made of insulating material, but I prefer to make them of high resistance metals or alloys, and the surfaces should be tarnished before assembling. If desired, the

rings 15 and 16 need'not be continuous rings, but open rings made by bending strips of metal about the rings 4.- and 5. The rings 7 and 8 should, however, be continuous rings, and should be shrunk on hot so as to make the aggregation mechanically equivalent to a single solid piece of metal. In Fig. 4 also the two parts 4- and 5 of the low resistance ring are shown held together by rivets 17. It is desirable, however, that the rings 4 and 5, as well as the bars 3, be soldered, brazed or welded to the resistor element 6.

As explained in the patents above referred to, the magnetic metals are best suited for use in the resistor element 6, since they exhibit a high positive temperature coeflicient of resistance, and in particular because they are characterized by an abrupt rise of resistance at a critical value of current. Iron has the advantage of cheapness and a high temperature coeliicient of resistance, while nickel possesses the advantage of greater resistance to oxidation at high temperatures. Iron coated with nickel affords the advantages of both. If it is desired to operate the resistor at temperatures above that at which oxidation even of nickel would occur, the portion 6 of the resistor may be coated with a film of heat resisting and non-oxidizing material. Gold is satisfactory for this purpose, and because of the small surface to be coated and the thin. film required, no serious expense is involved in the use of this material.

If desired, the inclosure 9 surrounding the resistor 6 can be substantially or hermetically sealed, the structure above described lending itself particularly well to such construction. In this way the resistor can be worked at much higher temperatures without injury to the protective coating, or without any such protective coating whatever, and thus a relatively great rise of resistance secured during the starting period.

Obviously, the resistor 6 can be given numerous other forms, as for example, a cylindrical form instead of the disk-like structure here shown, and it can also be made in sections instead of a single piece as here indicated.

I claim:

1. In an induction motor of the squirrel cage type, a short circuiting device comprising a low resistance ring not directly connected to the bars of the squirrel cage, and a resistor element interposed between and electrically and mechanically connected to both the low resistance ring and the bars of the squirrel cage, said resistor element consisting of a metal disk having a positive temperature coefiicient of resistance, and characterized by an abrupt rise of resistance at a critical value of current, and so proportioned" that the normal full load currents are below the-critical current value and the starting currents are above the critical value of current.

2. In an inductive motor of the squirrel cage type, a short circuiting device comprising a low resistance ring not directly connected to the bars of the squirrel cage, a resistor element of high positive temperature coefficient of. resistance interposed between and electrically and mechanically connected to both the low resistance ring and the bars of the squirrel cage, and rings of relatively high resistivity mounted on the said low resistance ring on each side of the said resistor element, and out of contact therewith for a short distance substantially as shown, one of said high resistance rings being mechanically connected to all of the bars of the said squirrel cage, and the surfaces of contact betweensaid rings having a high resistance.

3. In an induction motor of the squirrel cage type, a short circuiting device comprising a low resistance ring not directly connected to the bars of the squirrel cage, a resistor element of high positive temperature coeiiicient of resistance interposed between and electrically and mechanically connected to both the low resistance ring and the bars of the squirrel cage, and rings of relatively high resistivity mounted on the said low resistance ring on each side of the said resistor element, and out of contact therewith for a short distance substantially as shown, one of said high resistance rings being mechanically connected to all of the bars of the said squirrel cage, and the surfaces of contact between said rings having a high resistance by tarnishing.

4:. In an induction motor of the squirrel cage type,'a short circuiting device comprising a low resistance ring not directly connected to the bars of the squirrel. cage, a resistor element of high positive temperature coeilicient of resistance interposed between and electrically and mechanically connected to both the low resistance ring and the bars of the squirrel cage, and rings or" relatively high resistivity mounted on the said low resistance ring on each side of the said resistor element and out of contact therewith for a. short distance substantially as shown, one of said high resistance rings being mechanically connected to all of the bars of the said squirrel cage, the surfaces of contact between said rings having a high resistance, and said high resistance rings being firmly connected mechanically to the said low resistance rings.

5. In an induction motor of the squirrel cage type, a short circuiting device comprising a low resistance ring not directly connected to the bars of the squirrel cage, a resistor element of high positive temperature coel ficient of resistance interposed between and soldered to both the low resist ance ring and the bars of the squirrel cage, and rings of relatively high resistivity mounted on the said low resistance ring on each side of the said resistor element and out of contact therewith for a short distance substantially as shown, one of said high resistance rings being mechanically connected to each of the said bars by riveting, substantially as described, and the surfaces of contact between said rings having a high resistance.

6. In an induction motor of the squirrel cage type, a short circuiting device comprising low resistance ring not directly connected'to the bars of the squirrel cage, and a resistor element interposed between, and electrically and mechanically connected to both the low resistance ring and the bars of the squirrel cage, said resistor element consisting of a disk of metal having a positive temperature coefhcient of resistance, and those portions of said disk which are designed to be electrically connected to otaer parts being copper plated.

7. In an induction motor of the squirrel cage type, a short circuiting device comprising a low resistance ring, not directly connected to the bars of the squirrel cage, and a resistor element interposed between, and electri( ally and mechanically connected to both the low resistance ring and the bars of the squirrel cage, said resistor element consisting of a disk of metal having a positive temperature coeflicient of resistance, a portion of which is adapted to be heated to a high temperature by the starting currents in the rotor circuit, said heated portion being provided with apertures at frequent in tervals to permit expansion of the heated portion without warping.

8. In an induction motor of the squirrel cage type, a short circuiting device comprising a low resistance ring not directly connected to the bars of the squirrel cage, and a. resistor element interposed between and electrically and mechanically connected to both the low resistance ring and the bars of he squirrel cage, and means for inclosing that portion. of the resistor element adapted to be heated by the starting currents so as substantially to exclude circulation of air.

9. In an induction motor of the squirrel cage type, a short circuiting device comprising a low resistance ring not directly connected to the bars of the squirrel cage, and a resistor element interposed between, and electrically and mechanically connected to, both the low resistance ring and the bars of the squirrel cage, and means for inclosing that portion of the resistor element adapted to be heated by the starting current so as substantially to exclude circulation of air, said means comprising rings of high resistance material mounted on the said low resistance ring on either side of the said re sistor element and making close mechanical contact with the resistor element near its junction with the bars of the squirrel cage,

1'- the said high resistance rings having portions cut away adjacent to the heated portions of the said resistor element so as to be out of contact with the greater part of the heated portion.

10. In an induction motor of the squirrel cage type, a short circuiting device comprising a low resistance ring not directly connected to the bars of the squirrel cage,

and a resistor element interposed between, and electrically and mechanically connected to, both the low resistance ring and the bars of the squirrel cage a portion of said resistor being adapted to be heated by the starting currents of the motor, and means for hermetically sealing the inclosure surrounding the heated portion of said resistor element.

BURTON MCCOLLUM. Vitnesses T. LLOYD Mocimnnn, EDWIN S. CLARKSON.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents, Washington, I). C. 

